Method for kerfless cutting wood

ABSTRACT

To reduce splitting ahead of a knife a block of wood is cut by compressively stressing the wood to at least 25% of its yield strength, between clamps, then cutting the wood with a knife along a path between the clamps, releasing the clamps to remove the compression, and then separating the wood from the knife. Two or more knives may be used cutting in opposite or the same, parallel directions.

United States Patent [1 1 Johnston et al.

[ METHOD FOR KERFLESS CUTTING WOOD [75] Inventors: John S. Johnston; Andre St-Laurent,

both of Ottawa, Canada [73] Assignee: Canadian Patents and Development Limited, Ottawa, Canada [22] Filed: Jan. 22, 1975 [21] Appl. No.: 542,912

[52] US. Cl 144/309 D; 144/162 R; 144/193 D [51] Int. Cl. B27M 1/08; B27C 1/00 [58] Field of Search 144/309 R, 309 D, 312,

144/193 A, 193 D, 162 R [5 6] References Cited UNITED STATES PATENTS Veres et a1 83/14 Nov. 4, 1975 3,327,747 6/1967 Collins 144/309 R 3,494,396 2/1970 Collins 3,538,966 11/1970 Collins 144/162 R Primary Examiner-James L. Jones, Jr. Attorney, Agent, or FirmFra.ncis W. Lemon [57] ABSTRACT 7 Claims, 3 Drawing Figures US. Patent Nov. 4, 1975 v 3,916,966

METHOD FOR KERFLESS CUTTING WOOD This invention relates to a method for kerfless cutting wood.

One of the objectives of wood cutting research is to reduce the amount of sawdust resulting from the conversion of logs to lumber. The chipper-canter, now in widespread use, can eliminate sawdust completely up to the stage of the regular shaped cant, however cutting the cant into lumber still requires saws. Although saw kerf has been reduced greatly in recent years through research, the production of some sawdust is an unavoidable consequence of this type of cutting. In order to reach the goal of kerfless cutting, a tool other than the toothed saw must be used. One of the most promising of these is cutting with a knife, which is commonly called slicing.

Many attempts have been made to slice boards from logs or cants, using a rigid blade with wedge shaped cutting edge. The idea of using a single machine to slice a log completely into lumber of the required dimensions may seem attractive, however the problems in dealing with an irregular shaped object such as a log are very complex, and are perhaps avoidable in view of recent developments. A cant, of regular cross section and good dimensional accuracy, offers a much more attractive workpiece for slicing. Further, a great deal of lumber is produced from small logs in the form of studs, nominally 2 ins. X 4 ins. cross-section, 8 feet long: thus there would be an immediate application for a machine that could slice soft-wood cants, 4 ins. thick into studs.

When a wedge shaped tool is forced into the wood from the side or end of an unrestrained cant, uncontrolled splitting occurs ahead of the cutting edge because of tensile forces from the blade wedging effect. This may be counteracted to some extent by exerting compressive pressure at the cutting edge such as in the experiments by Peters et a1 as described in Slicing Wood One Inch Thick," Forest Products Journal, 19 (7), July 1969, Forest Products Research Society, 2801 Marshal Court, Madison, Wisconsin, USA; In these experiments slices 1 in. thick were cut from heated blocks of wood using a tool similar in shape to a veneer knife, and using a pressure bar as in veneer slicing. While splitting ahead of the cutting edge was controlled, fractures occurred parallel to the knife edge because the severed piece was required to bend by the blade wedging effect; further the 1 in. thick slice was curved as a result of the bending. It may be expected that the extent of fracturing would increase with thickness of the slice removed, and there would be little hope of removing 2 inch thick material in this manner.

It is an object of the present invention to provide a method for kerfless cutting wood with a knife wherein the tendency of the wood to split during cutting is substantially reduced.

According to the present invention there is provided a method for kerfless cutting wood comprising:

a. applying a clamping pressure to substantially the entire surfaces of two opposed sides of the wood so that it is compressively stressed to at least 25% of the yield strength of the wood,

b. cutting the wood with a knife along a path between the two opposed sides, while maintaining the clamping pressure on the wood,

c. removing the clamping pressure from the wood with the knife remaining in the wood, and

d. separating the wood from the knife.

In the accompanying drawings which illustrate, by way of example, embodiments of the present invention:

FIG. 1 illustrates the principle of an apparatus for carrying out the present invention, and

FIGS. 2 and 3 are perspective views illustrating different knife shapes which may be used.

Referring to FIG. 1, there is shown ahydraulic ram comprisinga base 1, a vertically extending bracket 2, a cylinder 4 containing a piston (not shown) and mounted in the bracket 2 and an anvil 6 attached by a rod 8 to the piston in the cylinder 4.

A knife 10 is mounted on the base 1 and another knife blade 12 is mounted on the anvil 6.

A horizontally extending bracket 14 passes through a clearance slot 16 in the base 1, to be movable therein, and extends beneath the knife 10. A cylinder 18 containing a piston (not shown) is mounted on one arm 20 of the bracket 14. A rod 22 attached to the piston in the cylinder 18 has a pressure pad 24 attached thereto. A pressure pad 26 is mounted on another arm 28 of the bracket 14.

In operation a block 30 of wood, say, 4 ins. X 4 ins. in cross-section is placed on the knife 10 and between the pressure pads 24 and 26, and the cylinder 18 is pressurized, by means not shown, to compress the block 30 so that it is compressively stressed to at least 25% of its yield strength over substantially its entire opposed sides.

The hydraulic cylinder 4 is then pressurized, by means not shown, to urge the knives 10 and 12 into the wood until the knives 10 and 12 meet and the wood is cut.

In experiments it was noted that as the knives 10 and 12 penetrated the wood there was an absence of cracks in the wood and that the annular rings in the wood were severely distorted close to the knives 10 and 12, as shown in FIG. 1.

It was also noted during slicing that the external surfaces of the block 30 remained substantially flat and in the same position. The block 30, being compressively stressed to at least 25% of its yield strength by the pressure pads 24 and 26, can only deform plastically to allow entry of the knives l0 and 12, and that this deformation occurs mostly just in front of the knives 10 and 12. Because of the cellular structure, solid material in the block 30 of wood occupies only part of the total external volume, for example about one quarter in the case of spruce, so that the knives 10 and 12 may be accommodated by simply compressing the wood near them. This differs from the deformation of relatively incompressible materials such as metals where a knife could not be inserted without changing the external dimensions of the block.

The bracket 14 being movable in the slot 16 in the base 1, allows the block 30 to move relative to the knives l0 and 12 and accommodate any bad positioning between the knives 10 and 12 and the block 30, prior to cutting, or to accommodate any nonhomogeneity of wood in the path of the knives l0 and 12.

The object of maintaining the compressive load is to limit tensile stresses developed in the wood during cutting to values lower than the tensile strength of wood in block 30 being cut. There will, of course be some compressive damage, but it can be localized, much of it will be recovered over a period of time after load removal.

Cutting trials, using apparatus which operated according to the principle illustrated in FIG. 1 were carried out in the laboratory. Blocks of green white spruce, 4 inches square in cross section, either 4 or 16 inches long, were sliced into two pieces, each 2 X 4 inches in cross section. The knives used were A inch thick and were sharpened as in FIGS. 2 or 3. For evaluating damage to the wood from the slicing action, any checking which extended /a inch deep from the cut surface was revealed by removing that thickness of wood from the surface by sawing.

Knives according to FIG. 2 were tested where Z A in., and the blade angles 6 20 and 45. Knives according to FIG. 3 were tested where x V8 in., Y 2 in., Z A in., and a 45.

During cutting, observation of the block ends showed that growth rings in the wood were severely distorted close to the knife, but no splitting ahead of the knife edge could be seen. It was also evident that cutting quality was better with sharper knives.

Of 30 short blocks cut by this method, 23 had no splits at a depth of one-eighth inch, the remainder had from one to four splits, which in all cases, were shorter than the block length.

Of 17 long blocks cut, five had no splits at '74; inch depth, 11 had one or two short splits, and one was split the full length at that depth.

No effect of lateral pressure magnitude was noted in these tests in the range of 150 to 300 psi.

In other exploratory slicings it seemed to make no difference to cut quality if the knives l and 12 penetrated closer to one side rather than in the center of the block 30. Furthermore the knife could penetrate from the end of the block 30 without splitting the wood. Slicings in dry spruce and in dry maple were also made successfully, with higher compressive loads corresponding to the wood strengths.

It was evident during these tests that the presence of knots in the wood affected both the accuracy of slicing and the extent of fracturing. Also the direction of annual rings relative to the cutting plane affected the depth and extent of checks.

From these cutting trials it was concluded that wood damage from the knife cutting action could be controlled and probably held to acceptable levels for structural lumber. Improvements in the quality of cutting may be expected as a result of further experimentation to optimize the cutting parameters.

In other embodiments of the present invention the wood is cut, while being compressively stressed as previously described, by:

l. A single knife being urged into one side or one end of the wood.

2. A row of knives being urged simultaneously into one side or one end of the wood to cut the wood into three or more pieces.

3. One side or one end of the wood being urged against a stationary knife.

4. One side or one end of the wood being urged against a row of knives to cut the wood simultaneously into three or more pieces.

5. Two opposed rows of knives moving towards each other to cut the wood simultaneously into three or more pieces.

In other embodiments the wood can be cut diagonally from an edge with a knife or row of knives inclined ,to the sides extending from that edge. The wood may be cut in this manner by opposed knives at diagonally opposed edged of the wood.

In yet other embodiments of the present invention the or each knife is longer than the face of the wood to be cut and the or each knife cuts the wood along say, a curved or sloping path, by a relative sliding motion between the or each knife on the one hand and the wood on the other. The sliding motion is in the longitudinal direction of the or each knife cutting edge and increases the cutting efficiency of the or each knife. It is necessary for the knife to be longer than the face of the wood so that the blade can be positioned with respect to the wood so that at any cutting position the knife cuts the wood the entire length of the face.

In other embodiments both of the pressure pads 24 and 26 (FIG. 1) are urged against the wood by pistons within cylinders so that the wood can more freely float during cutting to accommodate any bad positioning of the knife or knives prior to cutting or non-homogeneity of the wood in the cutting path or paths. For example if the knife or knives were wrongly positioned before the clamping pressure was applied then the freely floating wood can correct this mis-alignment.

In some instances it may be advantageous to impart a vibratory motion to the knife or knives to enhance the cutting action of the or each knife, in particular a reciprocating motion of the or each knife may be advantageous.

Instead of pressure pads 24 and 26 (FIG. 1), fluid pressurized hoses (e.g. hoses pressurized with water) may be used to compress the block of wood. Fluid pressurized hoses are particularly useful for compressing irregular surfaces.

If desired the sides of the block where the or each knife enters and leaves may also be compressed.

I claim:

1. A method for kerfless cutting wood, comprising:

a. applying a clamping pressure to substantially the entire surfaces of two opposed sides of the wood so that it is compressively stressed to at least 25% of the yield strength of the wood,

b. cutting the wood with a knife along a path between the two opposed sides, while maintaining the clamping pressure on the wood,

c. removing the clamping pressure from the wood with the knife remaining in the wood, and

d. separating the wood from the knife.

2. A method according to claim 1, wherein the wood is cut simultaneously by two opposed knives on opposite sides of the wood.

3. A method according to claim 1, wherein the wood is cut simultaneously into a least three pieces by a row of knives.

4. A method according to claim 1, wherein the wood is cut simultaneously into at least three pieces bytwo opposed rows of knives moving towards each other.

5. A method according to claim 1, wherein the wood is held stationary during the cutting and the knife is urged into the wood.

6. A method according to claim 3, wherein the wood is held stationary during the cutting and the row of knives is urged into the wood.

7. A method according to claim 1, wherein the wood, with the clamping pressure applied, is free to move in a direction across the blade to accommodate any misalignment between the knife and the wood and any non-homogeneity in the wood in the path of the knife. k 

1. A method for kerfless cutting wood, comprising: a. applying a clamping pressure to substantially the entire surfaces of two opposed sides of the wood so that it is compressively stressed to at least 25% of the yield strength of the wood, b. cutting the wood with a knife along a path between the two opposed sides, while maintaining the clamping pressure on the wood, c. removing the clamping pressure from the wood with the knife remaining in the wood, and d. separating the wood from the knife.
 2. A method according to claim 1, wherein the wood is cut simultaneously by two opposed knives on opposite sides of the wood.
 3. A method according to claim 1, wherein the wood is cut simultaneously into a least three pieces by a row of knives.
 4. A method according to claim 1, wherein the wood is cut simultaneously into at least three pieces by two opposed rows of knives moving towards each other.
 5. A method according to claim 1, wherein the wood is held stationary during the cutting and the knife is urged into the wood.
 6. A method according to claim 3, wherein the wood is held stationary during the cutting and the row of knives is urged into the wood.
 7. A method according to claim 1, wherein the wood, with the clamping pressure applied, is free to move in a direction across the blade to accommodate any mis-alignment between the knife and the wood and any non-homogeneity in the wood in the path of the knife. 